Piston-actuated tensioning devices of this nature with a restraint system are very common and are used in particular on internal combustion engines. The associated housing, together with a hollow cylindrical tensioning piston in the piston bore of the housing, forms a pressure cavity, which is normally filled with a hydraulic medium and in which a compression spring is arranged to tension the tensioning piston. Often tensioning devices of this nature have restraint systems in the form of latching mechanisms, which define a blocking and a slide-through direction for the tensioning piston, whereby retraction of the tensioning piston into the housing from a certain end-stop is prevented, but re-adjustment of the tensioning function is possible. A tensioning device of this nature is known, whereby the tensioning piston is provided with a sawtooth profile in which a ratchet block engages through a housing window. With this tensioning device the free working range of the tensioning piston is defined by the axial movement of the ratchet block in the housing window.
Tensioning devices with latching arrangements for limiting the inward movement of the piston and the simultaneous definition of a free working range of the tensioning device are very common and have been well-proven in use. However, a disadvantage with these tensioning devices is the complex structure which demands increased effort during the individual manufacture of the components and during the assembly, therefore implying higher costs.
At least one generic tensioning device is known. The tensioning piston of this hydraulic tensioner has a sawtooth profile in which two flexible latching arms of a latching element are clipped onto the housing from outside engage. Between the individual protrusions of the sawtooth profile larger distances are provided which define the free working range of the piston connected to the latching element, thus facilitating an axial movement of the tensioning piston with respect to the latching element along the free working range. When the tensioning piston enters the next latching point of the sawtooth profile, the rigid gradations due to the individual protrusions of the sawtooth profile and their spacing for provision of the free working range cause an abrupt increase in the forces acting on the flexible driving means. Consequently, only a smaller inward displacement into the piston bore remains, which is why no optimum damping against shocks and vibrations due to the driving means is available. The last groove of the sawtooth profile is formed as a stepped groove for limiting the maximum axial outward movement of the tensioning piston. With this tensioning device the working range of the tensioning piston, limited by the spacing of the individual protrusions of the sawtooth profile, was consequently found to be disadvantageous. Also in the contact region between the latching arms and the sawtooth profile of the tensioning piston and, due to the continuous axial movement of the piston in and against the tensioning direction, wear on the components of the latching arrangement occurs which can affect its operation.